The reason why there's articles that say Iran did it is because both the U.S and Iraq were blaming Iran at the time and were claiming that Iran had used them. But this claim was discredited and it was found to be a lie.

After the attack, the U.S said that a preliminary Defense Intelligence Agency (DIA) study had found that Iran was responsible and this study was also used by the CIA when Stephen C. Pelletiere, co-authored an analysis of the war itself where he also claimed that Iran was responsible for the attack.

Now, this went on for much of the early 90s. Which is why there's articles such as the one you linked from the 90s which reported this claim. And even up until 2003, Stephen Pelletiere was kind of claiming in a New York Times op-ed that this is what happened.

But the U.S never actually proved any of their claims, as they were unable to do so since it wasn't true. And when other groups looked into the incident, such as the Human Rights Watch when they conducted a two year study during 1992-1994, they found that it was in fact Iraq which had gassed the Kurds, not Iran. This stance has been reiterated by several groups since, such as Stockholm International Peace Research Institute in 2001.

And also it was also observed in 2003 by media that "Pelletiere's analysis for the CIA ignored evidence—including the recollections of hundreds of Kurdish witnesses; academic studies based on medical examinations, soil samples, and autopsies; and captured Iraqi government documents— which proved Iraqi culpability".

Iran was actually the first to report the attack to the world. And gave help and assistance to the Kurds at the time. In fact, Iran later went on to give asylum to about 1 million kurds who had fled Iraq because of the instability (Iran-Iraq War, Kurdish rebellions, Persian Gulf War etc.).

Now why would the U.S lie and do this? Well because they were actively supporting Saddam Hussein during the Iran-Iraq war, they knew that he was using chemical weapons against Iran and Iranians because he was losing (as seen by the declassified CIA files in 2013) and it obviously wouldn't be a good thing if the world found out that the American ally Saddam Hussein was using chemical weapons, especially against civilians.

TL;DR: No, Iran didn't gas the Kurds in the Halabja chemical attack. The U.S claimed that it was Iran because they didn't want people to know that their ally Saddam Hussein was using chemical weapons against civilians, but the U.S claim was discredited and it was found by several groups that Iraq was responsible.

Edit: Added tldr.